1. Field of the Invention
The present invention relates to a clock spring connector for use as an electric connection means in an air bag system included in a steering unit of an automobile.
2. Description of the Prior Art
A clock spring connector comprises a fixed member, a movable member attached rotatively around the fixed member, and a band-like flexible cable establishing the connection between the fixed member and the movable member. The clock spring connector has been widely used to serve as an electric connection means between a movable member and a fixed member that has a finite number of rotations, such as a steering unit of an automobile.
Since a clock spring connector of the foregoing type has the flexible cable, the cost of which being a very large portion of the overall cost of the clock spring connector, clock spring connectors each have been arranged to reduce the cost by shortening the flexible cable as disclosed in U.S. Pat. Nos. 4,540,223, 5,102,061 and so forth.
FIG. 23 is a plan view showing the schematic structure of the clock spring connector disclosed as described above. The clock spring connector shown in FIG. 23 comprises a movable member 101 rotatively disposed at the center of a cylindrical fixed member 100. The fixed member 100 and movable member 101 form an annular space 107 which accommodates a band-like flexible cable 102. The two ends of the flexible cable 102 are, while being respectively fixed to the fixed member 100 and the movable member 101, past to the outside of the annular space 107. The winding direction around the outer cylinder of the fixed member 100 and that around the inner cylinder of the movable member 101 are reversed in the annular space 107 at a position of a U-shape reversal portion 102a. In addition, an annular rotary plate 103 is disposed in the annular space 107 which has a planetary gear (omitted from illustration) pivotally supported to engage to gears respectively formed on the outer surface of the fixed member 100 and that of the movable member 101. On the other hand, the rotary plate 103 has, on the upper surface thereof, a plurality protruding shafts 104 located at predetermined intervals in the circumferential direction of the rotary plate 103. Each shaft 104 has a roller 105 freely rotatively attached thereto, and the reversal portion 102a is looped around one of the rollers 105.
When the movable member 101 of the thus constituted clock spring connector is rotated clockwise when viewed in FIG. 23, the reversal portion 102a is moved clockwise in the annular space 107 by a quantity of rotation which is smaller than that of the movable member 101. Thus, the flexible cable 102 is brought to a rewinding state in which a portion wound around the inner cylinder portion of the fixed member 100 become larger. Since the planetary gear (omitted from illustration) is, at this time, rotated and revolved in the annular space 107 due to the rotation of the movable member 101, a spacer 106 is moved clockwise at the same speed as that of the reversal portion 102a. As a result, the flexible cable 102 is smoothly moved in the annular space 107 without being pulled by the roller 105. The spacer 106 is a member including the rotary plate 103, shaft 104 and the roller 105. On the contrary, when the movable member 101 is rotated counterclockwise when viewed in FIG. 23, the reversal portion 102a is moved in the same direction by a quantity of rotation which is smaller than that of the movable member 101. As a result, the flexible cable 102 is brought to a wound state in which it is wound around the inner cylinder of the movable member 101 by a larger quantity. Also in this case, the spacer 106 is moved in the same direction at the same speed as that of the reversal portion 102a. As a result, the flexible cable 102 is smoothly moved in the annular space 107 without being pulled by the roller 105.
If the spacer 106 is moved by the flexible cable 102 because no planetary gear is provided, predetermined clearances have been required from a housing of the accommodating space 107, such as the ceiling surface and the bottom surface, to which the spacer 106 faces.
An automobile having the clock spring connector is easily affected the surface condition of a road or the like during running, and therefore vibrations of the automobile, of course, act on the clock spring connector. However, the conventional clock spring connector structured as described above and comprising the spacer 106 rotatively disposed in the accommodating space 107 has necessitates the forming of clearances between the spacer 106 and the ceiling surface of the accommodating space 107 in order for the spacer 106 to rotate smoothly. Therefore, if the axial vibrations of the steering shaft act on the clock spring connector, the spacer 106 is vertically vibrated in the clearance and thus it comes in conflict with both of the ceiling surface and the bottom surface of the accommodating space 107. Thus, there arises a problem of noise. Since the spacer 106 is typically made of hard plastic material, variations in the dimensional accuracy of each member and variations caused by temperature change or the like causes the clearance to easily be dispersed. Since a sufficient clearance has been given to cope with the dispersion, the problem of noise become critical.